fix bug division by 0

models/training_training.py

@@ -109,7 +109,9 @@ class Training(models.Model):
 
     @api.depends('student_ids', 'cost')
     def _compute_costs(self):
+        if self.students_count > 0:
             self.student_cost = self.cost / self.students_count
+        if self.hours_total > 0:
             self.rate = self.cost / self.hours_total
 
     @api.depends('session_ids')